BREACH WIDENING OBSERVATIONS RELATED TO CLAY CORE EARTHEN EMBANKMENT TESTS

Authors: Hunt, Sherry; Hanson, Gregory; Temple, Darrel

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2006
Publication Date: 9/10/2006
Citation: Hunt, S.L., Hanson, G.J., Temple, D.M. 2006. Breach widening observations related to clay core earthen embankment tests. In: Dam Safety 2006. Proceedings of the Association of State Dam Safety Officials Annual Conference, September 10-14, 2006, Boston, Massachusetts. 2006 CDROM.

Interpretive Summary: Many earthen embankment dams are reaching the end of their planned design and economic life. Over their service life, the landscape has changed due to urbanization; thereby, increasing runoff rates, reducing storage volumes of the reservoir, and changing the hazard classification of the structure in some cases. These changes may result in dam overtopping and potential subsequent breach. Research on dam breach has indicated that breach processes and rate are influenced by several factors including amount of flow over the top of the dam, the condition of the vegetal cover, and the type and placement of soil materials within the dam. Understanding how these variables relate to embankment breach can provide information that may be used to develop ways for predicting the time and rate of dam erosion and breach. Research using large-scale physical models of earthen embankments is on-going at the USDA-ARS Hydraulic Engineering Research Unit. The results from these tests are being used to support the development of computer models to predict breach. One embankment failure process of interest is breach widening and the release of the stored water in the reservoir. The objective of this paper is to contrast the time rate of breach widening of three large-scale earthen embankment tests. One embankment was constructed of a single soil type. The other two embankments were constructed of a combination of materials: one having a clay core section through the center of the dam, capped with a homogenous sandy material, and the other an inclined clay core section with a homogenous sandy material downstream. The embankments were 1.3 m in height with a 0.30 m notch through the center of the embankment. The results from these composite embankment tests as well as widening data from the previous homogeneous clay embankment widening test conducted at the laboratory show that rates of breach widening depended on the embankment geometry, soil type, and placement conditions of the embankment core materials. These test results will contribute to the development of a computer breach model.

Technical Abstract: Many earthen embankment dams are reaching the end of their planned design and economic life. Over their service life, shifting hydrologic conditions, hazard classification changes, sedimentation causing reduction in storage volumes, or a combination of these items has raised the concern for dam overtopping and potential subsequent breach. Research on embankment breach has indicated that breach processes and rate are influenced by several factors including hydraulic loading, embankment cover, embankment materials and configuration, and embankment geometry. Understanding how these variables relate to embankment breach can provide information that may be used to develop methodology for predicting timing and rate of embankment erosion and breach. Research using large-scale physical models of earthen embankments is on-going at the USDA-ARS Hydraulic Engineering Research Unit. The results from these tests are being used to support the development of numerical models to predict breach. One embankment failure process of interest is breach widening and the release of the stored water in the reservoir. The objective of this paper is to contrast the time rate of breach widening of three large-scale earthen embankment tests. One embankment was constructed of a homogeneous clay material. The other two embankments were constructed of composite materials: one simulating a clay core section through the center of the embankment, capped with a homogenous sandy material, and the other an inclined clay core section with a homogenous sandy material downstream. The embankments were 1.3 m in height with a 0.30 m notch through the center of the embankment. The results from these composite embankment tests as well as widening data from the previous homogeneous clay embankment widening test conducted at the laboratory show that rates of breach widening are strongly influenced by the embankment geometry, material type, and placement conditions of the embankment core materials. These test results will contribute to the development of a numerical breach model.